IMO subreddits like it are evidence that the Reddit macro model has been, and will continue to be a failure. The community is at its best when tone is actively directed by a dedicated mod team, and abusive behavior actively policed, in distinct contrast to the relative free-for-all that are the default subreddits.
Reddit's admins make a lot of noise about believing in the hands-off approach ("every man is responsible for his own soul"), but ultimately the hands-on approach create higher-quality communities (even at scale: see /r/iama) and curbs the abuse that has made the default subreddits complete intellectual wastelands. Not only that, Reddit itself has not been consistent on being hands-off, what with the banning of subreddits and whatnot.
Side shoutout to /r/movies - always good discussions. Things get more animated and sometimes less civil than /r/photography but the mod team does a good job keeping things from exploding.
http://reddit.com/r/hiphopheads
http://reddit.com/r/frugalmalefashion
http://reddit.com/r/javascript/
http://reddit.com/r/snowboarding/
I find these subs to be on topic, relatively positive, often receptive to the new and uninitiated, providing a wealth of FAQ/just starting out information and have interesting weekly events.
I especially enjoy the header with album release dates in hiphopheads, and there are a number of cool weekly events in frugalmalefashion (and its more expensive brother subreddit, http://reddit.com/r/malefashionadvice).
As with any sufficiently large group, you'll find groupthink. However, I've found that many smaller subreddits are more receptive of self-criticism when it gets too bad.
So I thought I'd take it into my own hands. Started posting content, inviting users who I thought would be interested, and almost 5 years later, turned into what it is today.
/r/mmfb
/r/leaves
/r/trichsters & /r/calmhands
/r/depression
/r/SuicideWatch
/r/Polandball (101,218 readers) is heavily moderated (important considering the jokes there easily invite real racism)
/r/ASoIAF (166,200 readers) and /r/gallifrey (38,643 readers) are examples of very good TV/book subreddits (A Song of Ice and Fire aka. Game of Thrones and Dr. Who). the mods work hard to keep the quality up but have the advantage of the "mainstream" subs /r/gameofthrones and /r/doctorwho which both gather most low-effort posts.
/r/diy
/r/mechanicalkeyboards
/r/woodworking
On the fence about categorizing /r/clojure and /r/ece as good. They're not awful, but they need more traffic to be "good". /r/ece is almost an informal 24x7 AMA for EE and CE and the rules are constantly being broken but not necessarily in a bad way (if that makes sense?)
There are subreddits I find interesting to read but probably miss the categorization of "good" by being rather subjective based on your personal opinions of the subject matter.
/r/futuresynth (no one comments but the stuff is great, nearly perfect ;))
/r/ada
/r/embedded
/r/raspberry_pi
/r/bicycling
/r/programming
/r/linux
/r/nottheonion
There are some subs I try to like /r/minimalism (which on any given day is either "I have nothing...but these apple products" or "Two arms..one too many?") and /r/zen which is mostly people arguing vehemently about what zen is (which is both ironic and often hilarious).
/r/motorcycles and /r/guns are good as well if you're into that sort of thing -- /r/guns is especially funny on the weekends ;)
I've thought about this for a while on and off and I'm not sure how you could scale that up in terms of moderation, some of the defaults do well while others are just a wasteground (I've also wondered if that is partially intentional in the sense of give the idiots a subreddit as a decoy).
I like reddit but it has it's shares of trolls and typical online negativity (which I actually dislike far more than the trolls they at least are easily spotted, the constant negativity wears you down).